This invention relates to a device for extending the range of peripheral bus, for example, a Universal Serial(trademark) (USB) Bus.
There is a need in the computer field to connect peripheral devices, such as keyboards, mice, cameras, printers, scanners, telephony systems, communications circuits, etc., to a host computer. The Universal Serial Bus (USB) was developed as a standardized, miniature, inexpensive interface for this purpose.
The USB comprises four wires. This gives four lines dedicated as follows:
Vbus (power), GND (ground), D+ (data) and Dxe2x88x92 (data).
The power and ground lines provide power from the host to the USB peripheral devices. The two data lines support bi-directional communications (half duplex) between the host computer and the USB peripheral device. Data is transferred in a bi-directional fashion in message packets.
The data lines are not fully balanced, and their performance is consistent with single-ended, unterminated lines. The maximum practical connection distance, dictated by the speed of the data communications, is limited to 5 meters. The data lines are tied to ground or power (Vbus) via pull up or pull down resistors at the host or USB peripheral device. At the host side, each of the two lines has the pull down resistor. At the USB peripheral device side, one of the two data lines has a pull up resistor depending on the speed characteristics of the device.
USB specifications are identified through two classes of device: full speed (for cameras and scanners), and low speed (for keyboards and mice). Low speed devices include a pull up resistor for the Dxe2x88x92 line. Full speed devices include a pull up resistor for the D+ line.
The USB standard supports a hub function. Hubs can be used to extend connection distances and/or connect several devices to a single host USB port. However, hubs inherently are asymmetric devices designed to be attached on one side to a host and on the other side to one or more peripheral devices. To the peripheral devices, the hub appears electrically as a host. They serve primarily to expand the number of USB ports and not extend the range of the peripheral bus over long distances.
An object of the invention is to provide a simple method of extending the range of a peripheral bus, such as a USB.
According to the present invention there is provided an arrangement for extending the range of a peripheral bus carrying message packets on at least one signal line, comprising a first extender device for connection to a first peripheral bus port, said first extender device serving as repeater for transferring signals to and from said first peripheral bus; a second extender device for connection to a second peripheral bus port, said second extender device serving as repeater for transferring signals to and from said second peripheral bus port; and a transmission medium for each said signal line on said peripheral bus interconnecting said first and second extender devices, whereby signals are directly transferred between the first and second peripheral bus ports over said transmission media without tracking the message packets.
In accordance with the principles of the invention, the signals on the bus are detected and directly transferred over a transmission medium to a like device which repeats them onto a similar bus. The extender devices do not attempt to read the message carried on the bus, but merely serve as repeaters transferring signals between the two extender devices.
The transmission medium is typically a transmission line, preferably a balanced transmission line, although it is possible that an unbalanced line can be used. The transmission line may be twisted pair, although other types of transmission line, such as optic fibres can be used. More generally, it is envisaged that RF and infrared transmission media can also be used.
Typically the terminal devices, known as bus extenders, detect the rising and trailing edges of the incoming signals.
The peripheral bus is typically a USB bus. In the specification, a USB bus includes a USB host or peripheral device. In other words, it will be understood that the extender can be connected directly to the peripheral device or host with USB support.
In a further aspect the invention provides a method of extending the range of a peripheral bus having a plurality of signal lines carrying message packets, comprising the steps of receiving incoming signals on said signal lines, and transmitting said signals on respective transmission media to a remote receiver without tracking said message packets.